Kovalev opened a nasty cut below Mikhalkin's right eye, which led to referee Steve Willis stopping the action.

This was Kovalev's first title defense since July 2016 when he defeated Isaac Chilemba on points in Russia.

In the co-main event, Dmitry Bivol knocked out Sullivan Barrera in the 12th round in his first defense of the WBA light heavyweight title.

Bivol (13-0, 11 KO's), 27, a Kyrgyzstan born fighter based out of Russia, had to overcome adversity. He was cut over the right eye in the second round from a headbutt, but went on to completely outclass one of the best 175-pounders in the division.